Abstract ? Transdisciplinary Research Methods Core The overarching goal of the Transdisciplinary Research Methods (Methods) Core is to support and train our investigators to make important discoveries that will move the field toward Ending HIV/AIDS among people who use drugs (PWUD). To make progress, research using state of the art designs and methods is needed to guide interventions and programs that will remove or lessen serious substance use-related disparities in HIV incidence and disease outcomes that stand in the way of achieving this goal. To promote the overall aims of the Center, the Methods Core has adopted these Specific Aims: 1) Support CDUHR affiliated investigators by providing training, seminars, and consultation on quantitative, qualitative and mixed approach research methods; 2) Ensure that the Center remains on the cutting edge of research and statistical methods; and 3) Ensure that new research methods are available to the larger field, particularly methods relevant to Ending HIV/AIDS in PWUD. To support CDUHR investigators to understand and apply sophisticated designs and methods to relevant research questions, the Core will provide a range of training and consultation activities, all of which are regularly adapted to the needs of our investigators. Core members are leaders in the fields of epidemiology, intervention science, statistical methods, qualitative research, and research using new technologies, and are joined by consultants and other senior CDUHR investigators who add expertise in other fields including mixed methods, adaptive intervention designs, agent-based modeling, social network analysis, and community participatory research.